dhcp4j is a pure Java DHCP parser, protocol manager, and server. It handles PXE options, vendor extensions, and the complete IANA database of known hardware types. It has network drivers written on Mina and Netty.

gradle-velocity-plugin is a gradle plugin for the Velocity template engine. It integrates the Apache velocity template engine into gradle, and solves your Version.java or version.h needs. You can also preprocess resources, if you like.

gradle-sablecc-plugin is a gradle plugin which creates parsers using SableCC. SableCC supports automatic CST-to-AST transformation, emits all the visitor patterns and analysis helpers you will likely ever need, and is LR, not LL(k). Many example grammars are available for modern languages; the author of this plugin has written dozens.

jdiagnostics is a library of routines for inspecting the state of a JVM and building a support bundle. It makes it easy to diagnose issues with classpaths, resources, serviceloaders, versioning, XML parsers, and so forth. It has no dependencies, and is an essential library to build into any infrastructure application.

Immutables allows you to embrace immutablity to tackle complexity and concurrency challenges. To get the benefits of immutability in Java, there's an annotation processor to easily create simple and consistent value objects. You can think of it as Guava's Immutable Collections but for regular objects. It includes support for JSON marshaling, MongoDB repositories, and JAX-RS.

Telepath provides map/reduce code for processing Wikipedia Pagecounts. These contain usage data for all Wikipedia pages in all languages on an hourly basis. Derived from the bakemono toolkit, this project can process this 3TB data set with ease.

jfuzzylite is a Java fuzzy logic control library. Its goal is to allow you to easily create fuzzy logic controllers in a few steps utilizing object-oriented programming without any third-party libraries.